Thermoset resins with hydroxy acrylate methacrylonitrile and blocked isocyanate

ABSTRACT

NOVEL THERMOSETTING RESIN POWDERS WHICH CAN BE MOLDED TO FORM PRODUCTS CHARACTERIZED IN TENSILE MEASUREMENT, BY HIGH ELONGATION-TO-BREAK, HIGH TENSILE STRENGTH AND MODULUS AND A HIGH GLASS TRANSITION TEMPERATURE ARE PREPARED FROM A MIXTURE OF (A) A PREPOLYMER FORMED BY REACTING (1) A HYDROXY ESTER OF ACRYLIC OR METHACRYLIC ACID AND A C2-C3 DIOL WITH (2) METHACRYLONITRILE OR ACRYLONITRILE OR A MIXTURE OF THE SAME, AND (B) BLOCKED DI- OR TRIISOCYANATE WHEREIN THE ISOCYANATE GROUPS ARE DIRECTLY ATTACHED TO AN AROMATIC RING AND DEBLOCK AT TEMPERATURES IN THE RANGE OF 120* TO 160*C.

y 2, 1972 s. s. LABANA 3,660,359

THERMOSET RESINS WITH HYDROXY ACRYLATE METHACRYLONITRILE AND BLOCKEDISOCYANATE Filed June 5, 1970 PPL POL V1145? 0F HYD/QOXY ACRYLA 7'5 METHACAVLO/V/TR/ZE CAPAOLACTAM BLOC/K50 TR/LSOCV/M/ATE CATALYST S T/PUCTl/fl/JL THE/9440557 By 9% gym United States Patent THERMOSET RESINSWITH HYDROXY ACRY- LATE, METHACRYLONITRILE AND BLOCKED ISOCYANATESantokh S. Labana, Dearborn Heights, Mich., assignor to Ford MotorCompany, Dear-born, Mich. Filed June 5, 1970, Ser. No. 43,893 Int. Cl.C08q 22/06 US. Cl. 26077.5 CR 18 Claims ABSTRACT OF THE DISCLOSURE Novelthermosetting resin powders which can be molded to form productscharacterized in tensile measurement, by high elongation-to-break, hightensile strength and modulus and a high glass transition temperature areprepared from a mixture of (a) a prepolymer formed by reacting (1) ahydroxy ester of acrylic or methacrylic acid and a C -C diol with (2)methacrylonitrile or acrylonitrile or a mixture of the same, and (b)blocked dior triisocyanate wherein the isocyanate groups are directlyattached to an aromatic ring and deblock at temperatures in the range of120 to 160 C.

THE INVENTION This invention relates to self-crosslinking, dry,thermosettable molding powders suitable for rapid curing processing asby compression and injection molding and applicable to the production ofrigid, tough, structural materials as, for instance, automobile bodypanels, electrical appliance housings, boat construction, storage tanks,conduits, particularly those for the transmission of heated fluids, etc.and to molded articles produced therefrom.

The thermosets of this invention, after molding, have a glass transitiontemperature above about 90 C., and preferably above 105 C. At roomtemperature (20"- 25 C.) these moldings exhibit, in tensile measurement,a strength in the range of about 7,000 to about 11,000 psi. or higher, amodulus in the range of about 400,000 to about 600,000 p.s.i. or higher,and elongation-to-break in the range of about 2 to about 6 percent orhigher.

Glass transition temperature is that temperature at which a glass-likematerial loses its rigidity and hardness and approaches the behavior ofan elastomer. More specifically, glass transition-.,temperature isdefined as the temperature at which such material shows a maximum in itsmechanical damping at low frequencies, e.g. about 1 cycle per second.

(1) Composition of the prepolymer The prepolymer, except for limitedsubstitution as hereinafter noted, is a copolymer of the following basiccomposition:

Wt. percent Hydroxy acrylate 25-40 Methacrylonitrile Balance The hydroxyacrylate components is a hydroxy ester of acrylic or methacrylic acidwith a C -C diol, e.g. hydroxy ethyl acrylate, hydroxy ethylmethacrylate, hydroxy propyl methacrylate, and hydroxy propyl acrylate.Acrylonitrile may be substituted in whole or in part for themethacrylonitrile but the latter is the preferred reactant in thatproducts produced from prepolymers containing this constituent and thecrosslinking agents used herein have a higher heat distortion (glasstransition) temperature than do the corresponding products usingacrylonitrile, all other factors being equal.

A minor portion of the methacrylonitn'le may be replaced with methylrnethacrylate to lower the melt viscosity. If styrene is substituted fora portion of the methacrylonitrile components, it should not exceedabout 10% of the same. Other acrylates and methacrylates are unsuitablefor this purpose. In the preferred embodiment, the hydroxy estercomponent comprises about 30 to about 36 weight percent of theprepolymer.

(II) Properties of the prepolymer The prepolymer has an averagemolecular weight in the range of about 3,000 to about 16,000, preferablyabout 6,000 to about 12,000. Less than about 5% of the molecules thereofshould have molecular Weight below about 1,000.

The prepolymer has a softening point in the rangeof about to about C.

(III) Preparation of the prepolymer The prepolymer is advantageouslyformed by solution polymerization using heat, a free radical initiator,and an inert solvent. The polymer is preferably recovered bycoagulation. Hexane, a mixture of hexane and toluene, etc., are suitablefor this purpose.

A free radical initiator is dissolved in the combined monomericreactants and is advantageously employed in an amount equal to about l-4Wt. percent of the combined monomer weight. Conventional free radicalinitiators are suitable for this purpose, e.g. acylperoxides, peresters,and azo compounds. Specific materials which have been used successfullyinclude 2,2 azobis (Z-methyl propionitrile), hereinafter termed AIBN,benzoyl peroxide hereinafter termed BPO, t-butyl perbenzoate andt-butylperoxypivalate.

As aforementioned, the reaction is carried out in an inert solvent, e.g.toluene, dioxane, methyl ethyl ketone, etc. Advantageously the weight ofthe solvent is equal to or in excess of the combined weight of thereactant and the initiator.

In a preferred method of preparation, the monomeric reactants and thefree radical initiator are added in small increments, e.g. dropwise, tothe solvent heated to reflux under nitrogen. When addition is complete,initiator in the amount of about 0.1% monomer weight is dissolved in asmall amount of solvent and added over a period of 20 to 60 minutes. Thereflux is then continued for about 2 hours. The prepolymer is thenrecovered by coagulation. This is preferably effected in the followingmanner: The reaction solution is further diluted with additional solventuntil the prepolymer comprises about 20-30 wt. per cent of the resultantsolution. This solution is then added slowly to a liquid that willelfect precipitation of the prepolymer. In this instance, hexane isquite suitable. A fine powder precipitates. This is recovered byfiltration, dried, and, if necessary, broken up by rolling or grinding.

In addition to the aforedescribed method of prepolymer preparation, theprepolymer can be formed by the wellknown techniques of emulsionpolymerization, bulk p0- lymerization and suspension polymerization.

(IV) Crosslinking agent LIN-( JR HNCOR IIN(lJOR CH2 CH2 This material iscommercially available (Isonate 123 P, The Upjohn Company, Kalamazoo,Mich.) in the form of a powder which has the following typical analysis:

Equivalent weight 246 Softening point, C. 90 Melting point, C. 130

Viscosity at 156 C., cps 1000 Other diand triisocyanates which aresuitable for use as crosslinking agents when blocked with caprolactamsare toluene diisocyanate, methylene diphenyl diisocyanate, thetriisocyanate obtained by reacting 3 moles of toluene diisocyanate with1 mole of trimethylol propane, etc. The blocking of isocyanates withcaprolactam is well known in the art and can be effected by blending thetwo materials with a suitable catalyst, e.g. triethylene diamine, inrefiuxing toluene.

Unblocked isocyanates effect crosslinking during the drying process andare not suitable for use in these molding powders. The usual blockingagents such as phenol, cresol, Z-butanol or furfural alcohol cannot beused because of their volatility.

The crosslinking agent is advantageously employed in sufiicient quantityto provide about 0.90 to about 1.10, preferably about 0.95 to about1.05, blocked isocyanate groups for each hydroxy group in the moldingpowder.

(V) Catalyst A catalyst is employed in the molding powder mix in theamount of about 0.1 to about 1% (basis weight of molding powder mix) tofacilitate the crosslinking reaction. Catalysts used for this reactionare triethylene diamine, i.e. Diazabicyclo 2.2.2 octane, hereinafterreferred to as DABCO triethylamine, N-methyl morpholine, organometalliccompounds such as stannous octoate, tetraphenyl tin, dibutyl tindilaurate, and inorganic compounds such as bismuth nitrate, stannicchloride and ferric chloride.

(VI) Additive It is within the scope of this invention to employ in themolding powder mix about 1.0 to about 10, preferably about 3 to about 7,weight percent (basis weight of molding powder mix) of a hydroxylatedreactive diluent having molecular weight below about 1,000 and having atleast two free hydroxyl groups. Suitable hydroxylated diluents includehydroxy terminated liquid polyesters, monomeric diols, e.g. ethyleneglycol, low (200-1000) molecular weight polyethylene glycols, etc.

It is also within the scope of this invention to employ up to about 1weight percent (basis weight of molding powder mix) of processing aids,e.g. zinc stearate, hydrogen wax, etc.

(VII) Preparation of the molding powder mix The powdered prepolymer, thecrosslinking agent, the catalyst, and the reactive or unreactiveplasticizer, when used, are dissolved in a suitable solvent, e.g.acetone, benzene, etc., and the solution is thoroughly stirred. Thesolvent is evaporated under vacuum leaving a rigid foam which is crushedto a fine powder. The powder is further dried under vacuum so that itcontains less than one percent of the solvent.

Alternatively, to the prepolymer solution as obtained by polymerizationare added crosslinking agent, reactive diluent, if any, and thecatalyst. The solution is stirred until homogeneous and then addedslowly to a vigorously stirred precipitating solvent such as hexane. Theprecipi tated powder is dried under vacuum. To ensure its homogeneity,the molding powder is passed through a roll mill at 50 to C. In lieu ofemploying the precipitation solvent and roll mill, one may merelyevaporate the solvent of the prepolymer solution.

Another method of preparing the molding powder consists of mixingtogether the powdered prepolymer, crosslinking agent, additives andcatalyst and homogenizing by passing through an extrusion mixer or aroll mill.

If desired, reinforcing fillers such as asbestos, glass fibers, claycalcium carbonate, calcium silicate, etc. may also be incorporated inthe molding powders. These fillers are useful to increase the strength,modulus and heat distortion temperature of the finished product.

The powders thus prepared are suitable for use in injection molding,compression molding, and transfer molding This invention will be morefully understood from the following illustrative examples whereintensile properties of the molded speciments are determined by TensileTest, American Society of Testing & Materials, D-638 (1961) with theoverall sample length at 2 inches and the parallel gauge section at /2inch.

The prepolymers in the foregoing examples have softening points betweenabout 100 and about C. The average molecular weights of the prepolymersin the foregoing examples are above about 3,000 and below about 16,000with less than 5% of the molecules thereof having molecular Weightsbelow 1,000.

EXAMPLE 1 In the following separate tests, the following procedure ofpreparation and test are used.

(1) mix monomers for prepolymer with reaction initiatOI.

(2) drop mixture (I) slowly into equal amount of re fiuxing toluene(unless other solvent designated) under nitrogen atmosphere withstirring.

(3) when addition (2) is complete add 0.1% initiator (basis weight ofreactants) in 15 ml. toluene to the stirred reaction mix 2).

(4) continue heating of the reaction mix for 2-3 hours.

(5 dilute reaction mix to 30% solids with toluene.

(6) coagulate prepolymer in 5-7 volumes hexane.

(7) recover prepolymer precipitate and dry same at 60 C. under vacuumfor 8 hours.

(8) mix resultant prepolymer powder with cross-linking agent andcatalysts in acetone.

(9) evaporate acetone under vacuum.

(10) mold (pressure 1500 psi.)

The materials for preparing the moldings and the test results of suchmoldings are set forth in the following table:

TABLE I.MOLDINGS AND PROPERTIES THEREOF Prepolymer Composition Moldingpowder Cure Properties HEMA Pre- Cross- Tem- Inltial polylinkingCatalyst pera- Te,

Per- MAN," mer, agent, ture, Time, Ts, per- 'lm, GTT, Number Grams centgrams Grams grains grams Grams F. min. p.s.i. cent p.s.1. C-

B 160 40 240 8 BPO 15 11.5 0.15 DABCO 370 15 8, 500 3.35 540, 000 113 6533 134 3 BPO 20 12. 2 0. 2 DABCO 360 15 9,800 5. 75 504, 000 110 260 32550 16 B P O 36 20. 0 0. 1 DAB 0 O 375 15 10, 600 4. 45 512, 000 98 26032 550 16 B P0 36 20. 0 0. 1 DAB CO 375 15 10, 025 4. 8 522,000 11 10733 25 230 30 BPO 50 2. 4 0. 2 DAB CO 350 7, 200 2. 5 426, 000 13 75 3325 230 30 BPO 15 7. l 0. 1 DABCO 375 8, 900 2. 8 472, 000 13 80 80 320 85. 7 0. 1 360 15 4, 820 11. 5 220, 60

1 Hydroxy ethy 1 methacrylate. 2 Methacrylonitrile, 3 Caprolactamblocked triphenyl dimethylene triisoeyanate; 4 Tensile strength;

Tensile e1 ongatlon-to-break; Tensile modulus;

[2.2.2] octane or triethylene diamine; time-would post cure to above 900.

EXAMPLE 2 Ihe procedures of Example 1 are repeated with the soledifference that an equimolar amount of acrylonitrile is substituted forthe methaerylonitrile in the prepolymer.

EXAMPLE 3 The procedures of Example 1 are repeated with the soledifference that in separate tests 25%, 50% and 75% of methacrylonitrilein the prepolymer is replaced with an equimolar amount of acrylonitrile.

EXAMPLE 4 The procedures of Example 1 are repeated with the soledifference that 10 percent of the methacrylonitrile in the prepolymer isreplaced with an equirnolar amount of methyl methacrylate.

EXAMPLE 5 The procedures of Example 1 are repeated with the soledifference that 25 percent of the methacrylonitrile in the prepolymer isreplaced with an equimolar amount of methyl methacrylate.

EXAMPLE 6 The procedures of Example 1 are repeated with the soledifference that 33 percent of the methacrylonitrile in the prepolymer isreplaced with an equimolar amount of methyl methacrylate.

EXAMPLE 7 The procedures of Example 1 are repeated with the soledifference that 45 percent of the methacrylonitrile is replaced with anequimolar amount of methyl methacrylate.

EXAMPLE 8 The procedures of Example 1 are repeated with the soledifference that the molding powder mix in each test contains 1 weightpercent ethylene glycol.

EXAMPLE 9 The procedures of Example 1 are repeated with the soledifference that the molding powder mix in each test contains 3 weightpercent of a liquid, hydroxy terminated polyester.

EXAMPLJE 10 The procedures of Example 1 are' repeated with the soledifference that the molding powder mix in each test contains about 10weight percent ethylene glycol.

EXAMPLE 11 The procedures of Example 1 are repeated with the soledifference that an equimolar amount of hydroxy ethyl acrylate issubstituted for the hydroxy ethyl methacrylate in the copolymer.

EXAMPLE 12 The procedures of Example 1 are repeated with the soledifference that an equimolar amount of hydroxy propyl methacrylate issubstituted for the hydroxy ethyl methacrylate in the copolymer.

7 Glass transition temperature; 11 Post cured at 350 F. for 60 minutes;

Diazabieyelo 12 Short cure time--would post cure to above 0.;

EXAMPLE 13 The procedures of Example 1 are repeated with the soledifference that an equimolar amount of hydroxy propyl acrylate issubstituted for the hydroxy ethyl methacrylate in the copolymer.

EXAMPLE 14 The procedures of Example 1 are repeated except that themolding powder mix contains 0.5 weight percent zinc stearate and theaverage molecular weight of the prepolymer is about 8,000.

EXAMPLE 15 A caprolactam blocked diisocyanate is prepared in thefollowing manner: to 1600 grams of refluxing toluene (-11l C.) are added300* grams of 4,4'-diphenyl methane diisocyanate, 226 gramscaprolactarn, and 0.5 gram diazabicyclo [2.2.2] octane. Heating iscontinued for 4 hours and the mix is allowed to cool. The blockeddiisocyanate is isolated and recovered by filtration.

The procedures of the preceding examples are repeated with the soledifference that a reactive equivalent amount of this diisocyanate issubstituted for the caprolactam-blooked triphenyl dimethylenetriisocyanate.

The foregoing examples are illustrative of the invention defined in theappended claims. Those skilled in the art will be aware thatmodifications may be made therein without departing from the scope ofthe invention as set forth in the appended claims.

I claim:

1.. A molding powder which comprises an intimate mixture of (a) acopolymer consisting essentially of about 25 to about 40 weight percentof a monohydroxy ester of a C -C diol and acrylic or methacrylic acidand a remainder consisting essentially of acrylonitrile,methacrylonitrile or a mixture thereof and having average molecularweight in the range of about 3,000 to about 16,000, and (b) acaprolactam-blocked dior tri-isocyanate, said isocyanate being presentin sufficient quantity to provide about 0.90 to about 1.10 blockedisocyanate groups for each hydroxy group in the molding powder.

2. A molding powder in accordance with claim 1 wherein said copolymercontains between about 30 and about 36 weight percent of saidmonohydroxy ester.

3. A molding powder in accordance with claim 1 wherein said remainderconsists essentially of methacrylonitrile.

4. A molding powder in accordance with claim 1 wherein said copolymerhas average molecular weight in the range of about 6,000 to about 12,000with less than about 5 percent of the molecules thereof having molecularweight below about 1,000.

5. A molding powder in accordance with claim 1 which contains betweenabout 1.0 and about 10.0 weight percent of a hydroxylated diluent havingmolecular weight below about 1,000 and at least two free hydroxy groupsper molecule.

61. A molding powder in accordance with claim 1 wherein said moldingpowder mix contains about 0.95 to about 1.05 blocked isocyanate groupsfor each hydroxy group in the same.

7. A molding powder in accordance with claim 1 wherein said isocyanateis selected from triphenyl dimethylene triisocyanate and 4,4'-diphenylmethane diisocyanate.

8. A molding powder which comprises an intimate mixture of (a) acopolymer consisting essentially of about 25 to about 40 weight percentof a monohydroxy ester of a C -C diol and acrylic or methacrylic acidand a remainder consisting essentially of a major portion ofmethacrylonitrile and a minor portion of methyl methacrylate and havingaverage molecular weight in the range of about 3,000 to about 16,000,and (b) a caprolactam-blocked dior tri-isocyanate, said isocyanate beingpresent in sufiicient quantity to provide between about 0.90 and about1.10 blocked isocyanate groups for each hydroxy group in the moldingpowder.

9. A molding powder in accordance with claim 8 wherein said copolymercontains between about 30 and about 36 weight percent of saidmonohydroxy ester.

10. A molding powder in accordance with claim 8 which contains betweenabout 1.0 and about 10.0 weight percent of a hydroxylated diluent havingmolecular weight below about 1,000 and at least two hydroxyl groups permolecule.

11. A molding powder in accordance with claim 8 wherein said copolymerhas average molecular weight in the range of about 6,000 to about 12,000with less than about 5 percent of the molecules thereof having molecularweight below about 1,000.

12. A molding powder in accordance with claim 8 wherein said isocyanateis triphenyl dimethylene triisocyanate.

13. A molded article having glass transition temperature above about 90C., tensile strength above about 5,000 p.s.i., tensile modulus aboveabout 400,000 p.s.i., and tensile elongation-to-break above 2 percentand formed from a molding powder which comprises an intimate mixture of(a) a copolymer consisting essentially of about to about 40 weightpercent of a monohydroxy ester of a C -C diol and acrylic or methacrylicacid and a remainder consisting essentially of acrylonitrile,methacrylonitrile or a mixture thereof and having average molecularweight in the range of about 3,000 to about 16,000, and (b) acaprolactam-blocked dior tri-isocyanate, said isocyanate being presentin sufficient quantity to provide about 0.90 to about 1.10 blockedisocyanate groups for each hydroxy group in the molding powder.

14. A molded article in accordance with claim 13 8 wherein saidmonohydroxy ester comprises between about 30 and about 36 weight percentof said copolymer and said copolymer has average molecular weightbetween about 6,000 and about 12,000.

15. A molded article in accordance with claim 13 wherein said isocyanateis selected from triphenyl dimethylene triisocyanate and 4,4'-diphenylmethane diisocyanate.

16. A molded article having glass transition temperature above about C.,tensile strength above about 7,000 p.s.i., tensile modulus above about400,000 p.s.i., and tensile elongation-to-break above 2 percent andformed from a molding powder which comprises an intimate mixture of (a)a copolymer consisting essentially of about 25 to about 40 weightpercent of a monohydroxy ester of a C C diol and acrylic or methacrylicacid and a remainder consisting essentially of a major amount ofmethacrylonitrile and a minor amount of methyl methaerylate and havingaverage molecular weight in the range of about 3,000 to about 16,000,and ('b) a caprolactam-blocked dior triisocyanate, said isocyanate beingpresent in sufficient quantity to provide about 0.90 to about 1.10blocked isocyanate groups for each hydroxy group in the molding powder.

17. A molded article in accordance with claim 16 wherein saidmonohydroxy ester comprises between about 30 and about 36 weight percentof said copolymer and said copolymer has average molecular weight in therange of about 6,000 to about 12,000 with less than 5 percent of themolecules thereof having molecular weight below 1,000.

18. A molded article in accordance with claim 16 wherein said isocyanateis selected from triphenyl dimethylene triisocyanate and 4,4'-diphenylmethane diisocyanate.

References Cited UNITED STATES PATENTS 3,245,941 4/1966 Mayer et al.26077.5 3,441,541 4/1969 DAncicco 260-775 3,028,367 4/1962 OBrien260-775 3,178,380 4/1965 Basel 260--77.5

DONALD E. CZAJA, Primary Examiner M. I. WELSH, Assistant Examiner US.Cl. X.R.

